The present invention relates to an optical disk (disc) recording/reproducing apparatus and method.
Particularly, the present invention relates to technology for reliably and stably performing a focus jump operation for moving among recording layers in an optical disk recording/reproducing apparatus (optical disk drive) able to record/reproduce data on a multilayer optical disk having two or more recording layers.
In an optical disk drive (optical disk recording/reproducing apparatus) able to record/reproduce on a multilayer optical disk having a plurality of recording layers, a focus jump operation is used to move a beam spot among the recording layers. This focus jump operation combines an acceleration pulse and a deceleration pulse to move an objective lens (object lens) to move the beam spot among the recording layers at a high speed. This operation method basically resembles a tracking jump operation moving among tracks in tracking servo control. Note that the jump direction of the focus jump operation is a jump among recording layers in the focus direction and differs from a tracking jump.
A tracking jump operation performed also in an embodiment of the optical disk recording/reproducing apparatus of the present invention will be explained. In the track jump operation, a tracking error signal TE varies in a sine wave state using time as a variable as illustrated in FIG. 1A, so the location of the beam spot with respect to the target track is correctly known and the timing of the acceleration/deceleration can be correctly given.
The pulse waveform illustrated in FIG. 1B shows that, for example, in order to drive a coaxial actuator 35 illustrated in FIG. 4 to move an objective lens 34 toward a target track, a tracking controlling means in a digital signal processor (DSP) 51 gives an acceleration pulse ACCE as a track jump drive signal TJdrv to the coaxial actuator 35 via a tracking driver 52 to accelerate the objective lens 34 moved in the tracking direction by the coaxial actuator, then the tracking controlling means in the DSP 51 gives a deceleration pulse DECCE as a track jump drive signal TJdrv to the tracking driver 57 to decelerate the movement of the objective lens 34 in the tracking direction.
In the focus jump operation for making the beam spot output from the objective lens 34 jump among the plurality of recording layers of the optical disk, as shown in FIGS. 2A and 2B, where making the focus jump from an n-th recording layer nL to an adjacent (n+1)-th recording layer (n+1)L, it is not easy to observe (detect) a change of both of a focus error signal FE and a summation signal RF other than at the vicinity of the recording layer, therefore, other than at the vicinity of the recording layer of the focus jump, it is difficult to accurately determine the timing of the acceleration/deceleration of the coaxial actuator so that the focus jump becomes stable. Therefore, as illustrated in FIG. 2C, the focus jump controlling means gives an acceleration pulse ACCE for driving the coaxial actuator as the focus jump drive signal FJdrv at a time t1, predicts the movement velocity of the objective lens at that time, and gives the deceleration pulse DECCE for driving the coaxial actuator 35 as the focus jump drive signal FJdrv at a time t2 after an elapse of a predetermined time when the focus error signal FE may exceed a threshold value FEth. Namely, the focus jump controlling means uses prediction to accelerate and decelerate the coaxial actuator in the vicinity of the target recording layer in the optical disk for the focus jump.
A disk drive (optical disk recording/reproducing apparatus) equipped with a focus jump function for performing the control method by such prediction has already been marketed as a DVD (digital versatile disk)-video player. The technology disclosed in for example Japanese Unexamined Patent Publication (Kokai) No. 10-143872, International Patent Publication No. WO98/05032, etc. has been used.
The technology disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-143872 uses a technique estimating a movement velocity of the objective lens mounted on an optical pick-up from when the focus error exceeds a certain level on an original recording layer before the focus jump to when it exceeds a certain threshold value on the target recording layer and generating a brake pulse as illustrated in FIGS. 2A to 2C.
In the technique disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-143872, however, when loading an optical disk having an inter-recording layer distance deviated from a reference in the optical disk recording/reproducing apparatus, an error occurs in the estimated movement velocity of the objective lens, so there is a possibility of the focus jump becoming unstable.
International Patent Publication No. WO98/05032 discloses technology for determining an amplitude of the brake pulse from the maximum value of a differential focus error signal.
In both techniques disclosed in Japanese Unexamined Patent Publication (Kokai) No. 10-143872 and International Patent Publication No. WO98/05032, the reflectance in each recording layer of the optical disk is correctly managed. These are techniques effective in a DVD-video player where a good S-curve is obtained for the focus error in each recording layer of a plurality of recording layers. In a disk drive system increasing the numerical aperture (NA) of the objective lens to achieving a higher density, however, the effect of aberration due to fluctuation of the substrate thickness of the optical disk becomes greater. For example, as illustrated in FIG. 3A, an S-curve having symmetric positive and negative characteristics for the focus error is obtained when the numerical aperture (NA) is small, but the positive and negative characteristics of the S-curve sometimes become asymmetric when the NA is large as illustrated in FIG. 3B. As illustrated in FIG. 3B, when the S-curve becomes asymmetric between positive and negative, the switching timing of the acceleration and deceleration of the coaxial actuator for moving the objective lens 34 in the focus direction cannot be correctly determined.
Further, in a writable optical disk drive for recording/reproducing, the reflectance in each recording layer of the optical disk also fluctuates, so with the method of determining the deceleration timing of the coaxial actuator by referring to the value of the S-curve of the focus error as in the tracking control, there is a possibility that a stable focus jump operation is not possible.